1. Field of the Invention
The present invention relates to a thin type image display device for use in a video apparatus, such as a color television receiver.
2. Description of the Prior Art
Relative to a system for realizing a thin type color television receiver, for example, there is proposed an image display device wherein a cathode serving as an emission source is disposed in a thin vacuum panel assembly composed of a front panel and a back panel, and electron beams are emitted from the cathode to excite a fluorescent member to thereby display a desired image.
In such a known device, a getter is employed for adsorbing residual gases (inclusive of gases generated from component elements) so as to maintain a proper pressure in the vacuum panel assembly. Since it is impossible to provide such a getter in any portion corresponding to the effective screen area, the getter is placed mostly in a peripheral region between the front panel and the cathode outside of the effective screen area.
However, if the getter is disposed in the periphery of the effective screen area, the portion other than the effective screen area is dimensionally increased to consequently reduce the substantial effective screen. There is also the disadvantage of diminution of the gas adsorption effect at the center of the screen, hence raising a problem with regard to deterioration of the image quality. To the contrary, if the portion other than the effective screen area is minimized, it is impossible to contain a sufficient amount of the getter required for maintaining the pressure so that satisfactory image quality is eventually not attained.
There is known another conventional thin type image display device as disclosed in Japanese Patent Laid-open No. Sho 60 (1985)-101844, wherein a space is formed between a cathode and a back panel, and some getter is contained in this space.
In the above device where the getter is disposed between the cathode and the back panel, a sufficient area of the effective screen can be ensured, and also a required amount of the getter can be contained for maintaining a proper pressure.
In the device mentioned, however, the getter is disposed behind the cathode on the reverse side with respect to the front panel where out-gases are mostly generated so that the out-gases at the center of the display screen cannot be adsorbed instantaneously due t the impediment induced by the cathode. Consequently it becomes impossible to maintain the proper pressure in the vacuum panel assembly, and there occurs deterioration of the cathode as well. Furthermore, the image quality is degraded at the center of the screen which eventually fails in attaining a higher image quality.
There also exists a disadvantage that a satisfactory vacuum pressure withstanding capability is not achievable since the cathode is supported merely at the outer periphery thereof. The above device is constructed so that the cathode is supported via a glass plate from behind by means of U-shaped spring members disposed at four corners of the back panel. However, such a structure is not exactly suited for ensuring a pressure withstanding capability and the cathode is prone to be broken as the pressure in the vacuum panel is rendered high, particularly in a large-sized display screen.